 Other methods include the use of almost-totally reflective mirrors at each end of the cavity, emitting the beam either by focusing it into a small hole drilled in the center of one mirror, or by redirecting through the use of rotating mirrors, prisms, or other optical devices, causing the beam to bypass one of the end mirrors at a given time.In its most common form, an output coupler consists of a partially reflective mirror, sometimes called a beamsplitter.The reflectance and transmittance of the mirror is usually determined by the gain of the laser medium.